There are a host of transmission systems which share the media for the transmission of information among a number of terminals and a server ranging from a satellite and ground stations, local and wide area networks, cable television networks and telephone networks. In an unshared communications medium, communication from the server to the terminals is affected by the server simply transmitting its data to the terminals in some systematic manner to ensure that data for each terminal is transmitted at some time. Conflict does not result since the server is the only initiator of data traffic in the server to terminal direction. This broadcasted data is available to all terminals. However, with the shared medium only one terminal may transmit to the server at any given instant in time. Various protocols have been developed to deal with this problem.
A protocol called ALOHA allows a terminal to transmit at will and retransmit if contention was detected. The transmitting terminal also has a receiver which simultaneously receives and analyzes the signal on the medium. If no other signal is present other than the one it is transmitting then no contention is present. But if the received signal is different than the one being transmitted then one or more other terminals are placing their transmission on the shared medium at the same time and contention is present. Each terminal retransmits with a different delay so that contention tends to be avoided amongst the terminals that were simultaneously transmitting. Variable delays, unpredictable response times, and low band width utilization of the medium are the drawbacks of this technique. Refinements, such as "slotted ALOHA" which alters the way retransmission is attempted, improve the channel utilization but delays are still variable. A polling protocol on the "slotted ALOHA" attempts to allows equal access to all terminals with predictable but longer delays and at the expense of lower utilization.
In satellite networks, Frequency Division Multiple Access (FDMA) is employed by which each terminal is assigned a unique frequency. This technique assists in overcoming the confusion problem due to contention but is still characterized by low utilization of the medium.
Are Accordingly, it is an object of the invention to provide an improved network for transmission of data amongst a plurality of terminals and a server. It is a further object of the invention to provide a solution that minimizes delays for real-time information. It is a further object to provide a network that has predictable delays for time sensitive information. It is yet a further object of the invention to provide a network that minimizes functionality requirements of a terminal while optimizing the cost/performance ratio.